(1) Field of the Invention
This invention is directed toward test fixtures, and more particularly to a test fixture for testing the shear strength of diffusion welds.
(2) Description of the Prior Art
Welding is a well known and commonly used technique for joining metals in configurations for use in supporting structures and the like. Because welding is used to fuse metals which will form a joint that will be subjected to various forces, it is important to know the strength of the weld. It is, of course, possible to calculate shear strengths and bending strengths based on engineering formulas and material properties. However, such formulas usually require a factor of safety so as to account for uncertainties in the material being used, the forces being applied and other unforeseen problems. Because of the uncertainties involved, it is helpful to back up the various formulas and the like with actual physical evidence. Therefore, actual physical testing of the metals or the like for acquiring test data under various circumstances is important in the design process. Therefore, it is desirable to use fixtures or the like to secure the metals and joints in question so that various forces can be applied to the same for determining their actual strength. Such fixtures are particularly important for determining the strength of welded joints, wherein such joints are frequently used for supporting loads in highly critical applications such as bridge trusses, building structures and automobile frames.
The fixture art includes support fixtures for testing the welded joints of articles of manufacture. However, these fixtures, as discussed below, are generally specifically designed for use with the particular articles of manufacture and not for general application to welded joints, as with the inventive fixture disclosed herein.
U.S. Pat. No. 4,012,947 to Tiegel discloses a method and apparatus for testing battery connector welds. In the manufacture of lead storage batteries, battery plates are used within the battery casing in an upstanding orientation. The battery plates must be electrically connected. This is frequently done by welding the plates together through an aperture in the plates. It is important to test the strength of these welds so that the electrical connections are maintained during use of the battery. The Tiegel invention includes the use of anvil and pressure members which bear against opposite edges of the lug projections of the battery. The anvil members engage the battery lug while the pressure member is used for providing a shear force against the immobile lug. The pressure member is forced in a shear direction via a pressure cylinder. If the weld joints successfully resist the shear force applied, the test is deemed successful and the weld joints of sufficient strength. The Tiegel tester is specifically designed for use with battery plate welds and could not easily be used with other test specimens, so that any weld could be tested for shear strength. It is generally unadaptable for use with testing weld joints in general.
U.S. Pat. No. 4,584,881 to Hogan discloses a weld testing head which is also directed for use in testing battery connections. In Hogan, an apparatus is provided which comprises a vertically movable main frame having a recess within a holding surface which is adapted for engagement with the top end of a lug. The lug is restrained from vertical movement. A secondary frame, slidably connected to the main frame, includes two horizontally movable clamping devices which have teeth for engaging the battery lug. The clamping devices are moved against the lug via pressurized cylinders. A vertically oriented pressure cylinder is also used for pulling the secondary frame upward while the clamping devices are engaging the battery lug. A pressure gauge is used to indicate the force being applied, and if the weld joint sustains, under a particular force, the weld joint is considered structurally fit. Similar to Tiegel, the Hogan invention has a particular design directed toward use with battery connector weld joints and lugs. In addition, the Hogan device depends upon the battery weight for providing a base from which to apply the weld testing device. The Hogan testing head engages the test subject via a horizontal clamping force. In using toothed clamps for accomplishing this, the Hogan device risks damage to the specimen being tested.
U.S. Pat. No. 3,566,681 to Iosipescu et al. discloses a shear testing apparatus directed for use with the testing of rocks and other building materials. The apparatus includes a pair of U-shaped calipers which are relatively positioned to form a rectangular enclosure for the insertion of a test specimen. The calipers include pressure members which can be adjusted to apply forces on the specimen in a shear direction. Accordingly, a major feature of the Iosipescu apparatus is the particular shape into which the rock or other building material is to be formed, wherein the particular shape allows for a known shear plane to be created within the specimen. The apparatus is adapted to be placed in an additional testing machine wherein the loads placed on the concrete or other material can be measured. Accordingly, the strength of the material can be determined based on the pressure applied at the point of fracture. The Iosipescu apparatus requires the formation of the specimen into a very unique shape that is obtainable because of the nature of the materials being tested. However, in testing weld joints between metals, it is both inefficient and difficult to shape the testing materials into particular designs simply for testing. Accordingly, the Iosipescu testing fixture is inappropriate for the tests to which the invention disclosed herein is directed.
There exists a need in the materials testing science for the efficient testing of the shear strength of welds between various materials, wherein the test fixture can be used to accurately test weld joint strengths removed from their operative configurations yet without having to arrange the materials in a complex design.